Re: VMs: Beinecke & MrSID...

[Gabriel Landini <G.Landini@xxxxxxxxxx>]

On Saturday 19 June 2004 07:16, Don Latham wrote:
> For the group's info: I looked into Mr Sid a couple of years ago for for
> another possible use. It is a Wavelet compression scheme that "matches" the
> pixels to the size of the "zoom" ie the farther in you zoom, the higher the
> pixel density. It's a very effective way to store a document. But if you
> want the most detail for say a whole page locally, the file will still be
> large.

Thanks for the info, Don. A bit of follow-up: unfortunately, like jpegs, the 
sid format is lossy, so converting from sid to tiff does not give the full 
resolution at that particular image size. It may *look* OK, but the 
compression artifacts are quite noticeable if one converts the image from RGB 
to HSB (hue, saturation and brightness format).

So there is no point in processing the tiff at that particular size. An 
alternative is to do some filtering and subsampling: to low-pass filter the 
image with a kernel of size similar to the artifacts  (in jpegs this is 8x8 
pixels, but I do not know for sids) and then reduce the image in size with 
interpolation/splines, etc.

I will try to find out a bit about the sid format and if I find a good set of 
parameters to do the above I will post here.

I guess that for Yale the other option -- loss-less compression using tiff or 
png formats -- would still have generated files which are too large for 
downloading. But in any case, these is the best set of images that were ever 
available. 
I wonder if they have uncompressed tiffs with the full resolution for sale.

Cheers,

Gabriel


______________________________________________________________________
To unsubscribe, send mail to majordomo@xxxxxxxxxxx with a body saying:
unsubscribe vms-list